It is easy to appreciate how a tiny change in anatomy resulting in capacity for speech would produce a huge change in behaviour. With language, it takes only a few seconds to communicate the message, 'Turn sharp right at the fourth tree and drive the male antelope towards the reddish boulder, where I'll hide to spear it. Without language, that message could be communicated only with difficulty, if at all. Without language, two proto-humans could not brainstorm together about how to devise a better tool, or about what a cave painting might mean. Without language, even one proto-human would have had difficulty thinking out for himself or herself how to devise a better tool.
I do not suggest that the Great Leap Forward began as soon as the mutations for altered tongue and larynx anatomy arose. Given the right anatomy, it must have taken humans thousands of years to perfect the structure of language as we know it—to arrive at the concepts of word order and case endings and tenses, and to develop vocabulary. In Chapter Eight I shall consider some possible stages by which our language might have become perfected. But if the missing ingredient did consist of changes in our vocal tract that permitted fine control of sounds, then the capacity for innovation would follow eventually. It was the spoken word that made us free. This interpretation seems to me to account for the lack of evidence for Neanderthal/Cro-Magnon hybrids. Speech is of overwhelming importance in the relations between men and women and their children. That is not to deny that mute or deaf people learn to function well in our culture, but they do so by learning to find alternatives for a spoken language that already exists. If Neanderthal language was much simpler than ours or non-existent, it is not surprising that Cro-Magnons did not choose to marry Neanderthals.
I have argued that we were fully modern in anatomy and behaviour and language by 40,000 years ago, and that a Cro-Magnon could have been taught to fly a jet aeroplane. If so, why did it take so long after the Great Leap Forward for us to invent writing and build the Parthenon? The answer may be similar to the explanation why the Romans, great engineers that they were, didn't build atomic bombs. To reach the point of building an A-bomb required two thousand years of technological advances beyond Roman levels, such as the invention of gunpowder and calculus, the development of atomic theory, and the isolation of uranium. Similarly, writing and the Parthenon depended on tens of thousands of years of cumulative developments after the arrival of Cro-Magnons—developments that included the bow and arrow, pottery, domestication of plants and animals, and many others.
Until the Great Leap Forward, human culture had developed at a snail's pace for millions of years. That pace was dictated by the slow rate of genetic change. After the Leap, cultural development no longer depended on genetic change. Despite negligible changes in our anatomy, there has been far more cultural evolution in the past 40,000 years than in the millions of years before. Had a visitor from outer space come to the Earth in Neanderthal times, humans would not have stood out as unique among the world's species. At most, the visitor might have mentioned humans along with beavers, bowerbirds, and army ants as examples of species with curious behaviour. Would the visitor have foreseen the change that would soon make us the first species, in the history of life on Earth, capable of destroying all life?
PART TWO
AN ANIMAL WITH A STRANGE LIFE-CYCLE
Chapter two traced our evolutionary history through the appearance of humans with fully modern anatomy and behavioural capabilities, but that chapter does not prepare us to go straight on to consider in more detail the development of human cultural hallmarks, such as language and art. That is because Chapter Two took up only the evidence of bones and tools. Yes, our evolution of large brains and upright posture was prerequisite to language and art, but that was not enough by itself. Human bones alone do not guarantee humanity. Instead, our rise to humanity also required drastic changes in our life-cycle, which will be the subject of Part Two of this book. For any species one can describe what biologists term its 'life-cycle'. That means traits such as the number of offspring produced per litter or birth; the interval between births; the parental care (if any) that offspring receive from the mother or father; social relations between adult individuals; how a male and female select each other to mate with; frequency of sexual relations; and longevity. We take the forms of these traits as they exist in humans for granted, as the norm, but our life-cycle is actually bizarre by animal standards. All the traits that I have just mentioned vary greatly between species, and we are extreme in most respects. To mention only some obvious examples, most animals produce litters much larger than one baby at a time, most animal fathers provide no parental care, and few other animal species live even a small fraction of three-score years and ten.
Of these exceptional features of ours, some are shared by apes, suggesting that we merely retained traits already acquired by our ape-like ancestors. For instance, apes too usually give birth to one baby at a time, have births spaced several years apart, and live for several decades. None of these things is true of the other animals most familiar (but less closely related) to us, such as cats, dogs, songbirds, and goldfish.
In others of these respects, we are greatly different even from apes. Here are some obvious differences whose functions are well understood. Human babies continue to have all food brought to them by their parents even after weaning, whereas weaned apes gather their own food. Most human fathers as well as mothers, but only chimpanzee mothers, are closely involved in caring for their young. Like seagulls but unlike apes or most other mammals, we live in dense breeding colonies of nominally monogamous couples, some of whom also pursue extramarital sex. All these traits are as essential as large brain-cases for the survival and education of human offspring. That is because our elaborate, tool-dependent methods of obtaining food make weaned human infants incompetent to feed themselves. They first require a long period of food-provisioning, training, and protection—an investment much more taxing than that facing the ape mother. Hence human fathers who want their offspring to survive to maturity have generally assisted their mate with more than just sperm, the sole parental input of an orangutan father. Our life-cycle also differs from that of wild apes in more subtle respects whose functioning is nevertheless still discernible. Many of us live longer than most wild apes: even hunter-gatherer tribes include some elderly individuals who are enormously important as repositories of experience. Men's testes are much larger than those of gorillas but smaller than those of chimps, for reasons that will become apparent in Chapter Three. We regard human female menopause as inevitable, and Chapter Seven will show why it makes good sense for humans, but it is almost unprecedented among other animals. The closest mammalian parallel is among some tiny mouselike marsupials in Australia, and it is their males, not their females, that undergo menopause. Our longevity, testis size, and menopause were thus also prerequisites to our humanity. Still other features of our life-cycle differ far more drastically from those of apes than do our testes, yet the functions of those remaining novel features of ours remain hotly debated. We are unusual in having sex mainly in private and for fun, rather than mainly in public and only when the female is able to conceive. Ape females advertise the time when they are ovulating; human females conceal it even to themselves. While anatomists understand why men's testes are the size that they are, an explanation for men's relatively enormous penis still escapes us. Whatever their explanation, all these-features, too, are part of what defines humanity. Certainly, it is hard to picture how fathers and mothers could cooperate harmoniously in rearing their children if human females resembled some primate females in having their genitalia turn bright red at the time of ovulation, becoming sexually receptive only at that time, flaunting their red badge of receptivity, and proceeding to have sex in public with any male in the vicinity. Human society and child-rearing rest therefore not only on the skeletal changes mentioned in